Do teachers mention test scores at all in a recommendation letter? My teacher is asking for my highest ACT right now but I will be retaking it so I don’t want her to mention my old score in the letter 
They don’t usually and probably shouldn’t–it will be in your transcript anyway. Maybe the teacher just want to know to help get a better feel for you as an applicant?
Just tell her what it is now and that you intend to retake.